1. Field of the Invention
The present invention relates to a sheet with movable contacts and a sheet switch using the same, which are for use in operating panels of various electronic devices for example.
2. Description of the Related Art
A conventional structure of a sheet with movable contacts and that of a sheet switch are shown in FIGS. 5 to 8, of which FIG. 5 is an exploded perspective view of the sheet with movable contacts, FIG. 6 is a sectional view thereof, FIG. 7 is an exploded perspective view of the sheet switch, and FIG. 8 is a sectional view thereof.
In those figures, the sheet with movable contacts is made up of movable contacts 23 formed in a dome shape using metal, a sheet 21 formed by an insulating film, the sheet 21 covering upper surfaces of the movable contacts 23 and having an adhesive 22 applied to a lower surface thereof, and a separator sheet 24 affixed to the lower surface of the sheet 21 to close lower surfaces of the movable contacts 23, the separator sheet 24 being formed by paper or an insulating film.
The domed upper surfaces of the movable contacts 23 are covered with and fixed to the adhesive 22 which is applied to the lower surface of the sheet 21. The separator sheet 24 affixed to the lower surface of the sheet 21 is for preventing corrosion of the movable contacts 23 caused by gases contained in air or for preventing the adhesion of foreign matters to the movable contacts, during storage or transport of the sheet. The separator 24 can be peeled off.
The sheet switch is made up of the above sheet with movable contacts and a circuit board 28 provided on an upper surface thereof with central fixed contacts 30 and outer fixed contacts 29. In a removed state of the separator sheet 24 from the sheet with movable contacts, the movable contacts 23 are affixed onto the circuit board 28 using the adhesive applied to the lower surface of the sheet 21 in such a manner that lower ends of outer peripheries of the movable contacts 23 are respectively brought into abutment with the outer fixed contacts 29 and that central portions thereof are opposed to the central fixed contacts 30.
In the above structure of the sheet switch, when an operating portion 31a of a rubbery or resinous push-button 31 disposed above the sheet switch is depressed, the associated movable contact 23 is depressed by a depressing portion 31b formed on a lower surface of the operating portion 31a and is inverted, so that its central portion comes into abutment against the associated central fixed contact 30 on the circuit board 28, whereby the central fixed contact 30 and the associated outer fixed contact 29 on the circuit board are electrically connected with each other. Upon release of the depressing force imposed on the push-button 31, the central portion of the movable contact 23 is disconnected from the central fixed contact 30 with an elastic restoring force of the movable contact.
In the above conventional structures of the sheet with movable contacts and the sheet switch, however, the movable contacts 23 are covered with and fixed to a single sheet 21 of an insulating film with the adhesive 22 applied to the lower surface of the sheet, so when the sheet with movable contacts is affixed onto the circuit board 28 and when any of the domed movable contacts 23 located near the outer periphery of the sheet 21 is depressed, the air present within the dome of the movable contact is forced out and causes an end portion of the sheet to float, thus giving rise to the problem that dust enters through the floating end portion and causes an incomplete state of contact.
Moreover, the portions of the sheet 21 which surround the domed movable contacts 23 are fixed with the adhesive 22, so when any of the movable contacts 23 is depressed, the air present within the dome of the depressed movable contact cannot escape anywhere, thus giving rise to the problem that the operation feeling is deteriorated.
Accordingly, it is an object of the present invention to solve the above-mentioned problems and provide a structure of a sheet with movable contacts and a structure of a sheet switch using the sheet which, even when a movable contact located near an outer periphery of the sheet is depressed, can prevent floating of the sheet and can thereby prevent the entry of dust, thus affording a high contact reliability, and which can afford a good operation feeling at the time of operation and a superior adhesion between the movable contacts and a sheet member applied over the movable contacts.
For solving the above-mentioned problems, according to one aspect of the present invention, there is provided a sheet with movable contacts, comprising a first sheet formed by an insulating film, the first sheet having an adhesive surface formed by applying an adhesive to a lower surface of the first sheet, a plurality of domed, metallic, movable contacts whose upper surfaces are covered with and affixed to the adhesive surface of the first sheet, and a second sheet formed by an insulating film, the second sheet being affixed to the lower surface of the first sheet and having a plurality of receptacle holes for receiving the movable contacts therein, with an adhesive being applied to a lower surface of the second sheet, wherein the second sheet has connecting slots formed therein for connecting adjacent such receptacle holes with each other.
In another aspect of the present invention, a separator sheet whose upper surface has been subjected to a release treatment is affixed to the lower surface of the second sheet so as to be releasable from the second sheet.
In a further aspect of the present invention, through holes are formed in the separator sheet opposedly to the plural receptacle holes formed in the second sheet, and a protective sheet is affixed to a lower surface of the separator sheet to close the through holes.
In a still further aspect of the present invention there is provided a sheet switch comprising the sheet with movable contacts first referred to above and a circuit board having a plurality of fixed contacts, wherein, with the movable contacts arranged opposedly to the fixed contacts, the sheet with movable contacts is affixed onto the circuit board with the adhesive applied to the lower surface of the second sheet.